The invention relates to gas lasers, and more particularly to a power supply for a gas laser wherein a high ionization voltage is efficiently produced, for initially starting the laser, while a much lower operating voltage is supplied after the laser has started.
It is important in most laser installations that the current to the laser be held constant, so that the power output of the laser is relatively constant. Gas lasers require a more or less constant operating current even to function at all, and are especially sensitive to minor operating current variations.
In lasers used in bar code scanners, the edges between the light bars and dark bars on the bar code must be detected, and this amounts to detecting a difference in power level with associated detector circuitry of the scanner. In such devices if the laser tube power level itself is fluctuating, this could make it appear to the rest of the electronic systems that a label is being read, i.e. that edges between light and dark are being detected.
Therefore, particularly in laser scanner applications, it is very important that the power supply or the laser supply current be at a constant level to the laser, to produce a beam of constant output power.
Gas lasers generally require a very high ionization voltage for starting the laser, as compared to the much lower voltage required for normal operation of the laser after it has started. Prior to the present invention, the high ionization voltage was supplied by providing a larger power supply or by using a series of stages for multiplying the voltage for starting, with the multiplier stages inoperative when the laser is in a normal operating mode. These multiplier stages, which can be up to four or five stages in some applications, require a high parts count in the circuitry and correspondingly increased cost and space requirements.